Silyl substituted chloramphenicol



United States Patent 3,442,926 SILYL SUBSTITUTED CHLORAMPHENICOL Ronald L. Houtman, Parchment, Mich., assignor to The Upjohn Company, Kalamazoo, Mich., a corporation of Delaware No Drawing. Filed Aug. 31, 1966, Ser. No. 576,239

Int. Cl. C07f 7/18; A61k 27/00 US. Cl. 260448.8 3 Claims H NH-O 0 011012 Nori;ioligon It has been shown to have beneficial anti-infective properties against gram-positive and gram-negative organisms, mycoplasma and rickettsiae. However, chloramphenicol is noticeably bitter to the taste. Also, in parenteral pharmaceutical applications, such as subcutaneously and intramuscularly, there has existed a problem of obtaining sufliciently prolonged blood levels of the active substance.

It has now been found, in accordance with the present invention, that the aforesaid unsolved problems in the prior art are ameliorated by preparation and use of silyl ethers of chloramphenicol. These silyl ethers, in essentially pure crystalline form, not only retain the beneficial anti-infective properties and uses of chloramphenicol but provide improvement thereover, especially in respect to nonbitterness to the taste in suspension and activity when administered parenterally, for example in sterile vegetable oil solutions in which chloramphenicol is insufliciently soluble and in aqueous suspensions. Previously, vapor phase chromatography of trimethylsilyl derivatives of compounds related to chloramphenicol has been described without isolation of essentially pure crystalline compounds or awareness of any beneficial anti-infective properties. Shaw, Analytical Chemistry, vol. 35, No. 11, 1580-1582, October 1963.

Hence, the present invention provides as novel and useful compositions of matter, compounds represented by the formula whrein R and R are selected from the group consisting of lower alkyl containing 1 to 6 carbon atoms, inclusive, phenyl and benzyl, and R is selected from the group consisting of lower alkyl containing 1 to 6 carbon atoms, inclusive, phenyl, benzyl and hydrogen; and R is selected from the group consisting of hydrogen and the moiety wherein R R and R are as given.

Generally described, the manner and process of making the inventive compositions of matter is to react chloramphenicol with a silylating agent in a suitable solvent for 3,442,926 Patented May 6, 1969 the reactants and thereafter recover the silyl ether. A suitable solvent is pyridine, preferably anhydrous. The relativereactivity of the primary and secondary hydroxyl groups of chloramphenicol is such that the former is first silylated preferentially to yield silyl ethers in which R is hydrogen and R is the moiety a SiR4 given above, for example H NEE-000E01 Both hydroxyl groups are silylated by use of excess silylating'agent, for example, the bifunctional agent hexamethyldisilazane, with trimethylchlorosilane as a catalyst. Silylatior i of both hydroxyl groups occurs readily at ambient temperature, resulting in the formation of the di(trimethylsilyDether. The disubstituted others are readily converted to the monosubstituted ethers, wherein R is hydrogen and R' is the moiety given above, for example bis-O-(trim'ethylsilyl)chloramphenicol to the mono-O-(trimethylsily'l) compound, under mildly acidic conditions, for example 0.4% acetic acid in methanol.

Other operable silylating agents not requiring the presence of a catalyst are known, for example diorganomonochlorosilanes such as diphenylmonochlorosilane, dibenzylmonochlorosilane, methylphenylmonochlorosilane, ethylphenylmonochlorosilane, and ethylbenzylmonochlorosilane, as in British Patent 822,970, referred to in Chemical Abstracts 44:658 (1950). Trisubstituted chlorosilanes from trimethyl to tribenzyl are known, synthesized by the action of limited amounts of the appropriate Grignard reagent on the silicon tetrahalide. Successive treatment with different Grignard reagents yields mixed trialkyl chlorosilanes. Cram and Hammond, Organic Chemistry, p. 257 (1959) and Sneed and Brasted, Comprehensive Inorg. Chem. 7: 111-112 (1958). Organosilanes are also described in Roberts and Caserio, Basic Principles of Org. Chem., pp. 1182-1184 (1964). Silylation With the monofunctional agents goes readily without a catalyst being present.

For the purification of the ethers, the preferred method is to concentrate the reaction mixture to dryness and take up the residue in chloroform. The chloroform solution is washed thoroughly with water, and after the water phase is separated, the chloroform phase is filtered through silica gel. The filtered chloroform solution is evaporated to dryness to yield the purified crystalline silyl ether.

The following examples set forth how to make and use the present invention and the best mode contemplated of carrying out the invention but are not to be construed as limiting.

Example I.-Bis(trimethylsilyl)ether of chloramphenicol 40 gm. of chloramphenicol is dissolved in 50 ml. of anhydrous pyridine. Silylation is accomplished by adding 200 m1. of hexamethyldisila-zane and ml. of trimethylchlorosilane and allowing the reaction to proceed at room temperature for about 2 hours. One liter of chloroform is added to the reaction mixture and the whole is then washed with water for about three hours to remove any impurity. After separation of the aqueous phase, the remaining chloroform solution is filtered through a silica gel pad to remove polar impurities. Thereafter, the chloroform solution is taken to dryness to yield 52.0 gm. of the essentially pure crystalline ether.

Analysis.Calcd. for C H Cl N- O Si C, 43.68; H,

3 6.04; N, 5.99; CI, 15.17. Found: C, 43.42; H, 6.09; N, 5.85; C1, 15.15.

[0.]D (EtOH) +5 U.V. (EtOH) x 6 subcutaneously in mice, the CD v. Pasteurella maltocida is 21 mg./kg. (base equivalent being 15 mg./kg.). Orally the CD is 15 mg./kg. (base equivalent being 10 mg /kg.). These activities represent substantial superiority over chloramphenicol controls.

Given orally in suspension to rats at a level of 500 mg./kg. for 5 days, the compound is well tolerated as measured by body weight, food conversion ratio, hemo grams and gross pathological examination. The calculated LD in mice intraperitoneally is 4123 mg./kg.; in rats orally it is 4000 mg./kg.

Depending upon the solvent used in recrystallizing the compound to essentially pure crystalline state, two crystal modifications are obtained:

Form I.The crystal modifications upon crystallization from chloroform; a mull thereof in refined mineral oil exhibiting the following absorption bands in the infrared, in reciprocal centimeters:

4 Band: Intensity Band: Intensity 1312 W 755 M 1291 W 745 M 1272 W 720 W 1260 M 700 W 1250 S 690 W 1234 W 675 W Example 2.--M0n0(trimethylsilyl) ether of chloramphenicol 10 gm. of the product of Example 1 is dissolved in 250 ml. of methanol containing 0.4% acetic acid. The reaction mixture is stirred for 16 hours. Thereafter, the whole is evaporated to dryness and the residue is taken up in chloroform. The chloroform solution is Washed several times in water, the aqueous phase separated, and the chloroform solution is taken to dryness to yield 8.1 gm. of the mono(trimethylsilyl)ether, essentially pure and crystalline.

Analysis.Calcd. for C H Cl N O Si: C, 42.54; H, 5.10; N, 7.09; Cl, 17.94. Found: C, 42.50; H, 5.14; N, 7.33; Cl, 17.85.

Band: Intensity Band: Intensity [111D (EtOH) +9 U.V. (EtOH) A e 3265 M 1253 S sh. 214 11,450 3070 W 1218 W 272 9,750 3010 M 1197 M 2950 1 S 1175 W subcutaneously in mice the CD v. Pasteurella multo- 2920 S 1112 S cida is 30 mg./kg. (base equivalent being 27 mg./kg.). 2850 1 S 1105 S Orally the CD is 17 mg./kg. (base equivalent being 15 1695 S 1097 S mg./kg.). The subcutaneous activity represents substantial 1670 S 1070 S superiority over a chloramphenicol control. 1643 W 1030 S Given orally in suspension to rats at a level of 500 1609 M 1013 M mg./kg. for five days, the compound is well tolerated as 1603 M 960 W measured by body weight, food conversion ratio, hemo- 15 60 M 900 M grams; and gross pathological examination. The calculated 1545 S 870 S LD in mice intraperitoneally is 684 mg./kg.; in rats 1523 S 845 S orally it is 4000 mg./kg. 1492 W 812 S Ethcrification is at the secondary hydroxyl (R Nu- 1460 1 M 800 M clear magnetic resonance supports the structure. A mull 1417 W 750 S in refined mineral oil exhibits the following absorption 1375 1 M 723 M bands in the infrared, in reciprocal centimeters. 1346 S 700 M Band: Intensity Band: Intensity 1314 M 675 M 3405 s 1195 w 1288 W 665 M 3380 s 1176 w 1254 S 3105 w 1116 M 1 1 3065 W 1106 S 3040 W 1085 S Form II.-The crystal modification upon crystalliza- 5 1 1050 3 tion from ethanol; a mull thereof in refined mineral oil 2920 1 S 1030 S exhibiting the following absorption bands in the infrared, 5 1 S 1015 M in reciprocal centimeters: 7 0 w 970 w Band: Intensity Band: Intensity 05 W 5 W 3375 S 1219 W 1 2 S 39 M 3105 W 1211 W 1609 M 73 S 3070 W 1195 W 1 00 M 35 S 2950 S 1170 W 1525 s 4 M 2920 S 1123 M 0 49 w 829 M 2850 S 1111 M 14 M 0 M 1697 S 1105 M 1459 1M 7 W 1606 M 1100 S 1415 M 770 M 1594 W 1090 S 1375 1W 750 S 1561 W 1070 S 1347 s 725 w 1533 S 1035 M 1313 M 702 M 1518 S 1 8 W 129 1 M 90 W 1484 W 9 9 W 1255 s 7 w 1465 M 9 5 W 120 M 47 M 1415 W 9 0 W 1322 33:31:: ll 39? 3:31:33: 2 Example34121041011121)ether 1375 W 821 M 100 mg. of chloramphenicol is dissolved in 10 ml. of 1344 S 805 M anhydrous pyridine. 2.4 gm. of triethylchlorosilane is 1320 W 790 M added and the reaction mixture is allowed to stand at Example 4 .-M ono triethylsilyl ether The -bis(triethylsilyl) ether of Example 3 is converted into the corresponding mono(triethylsilyl)ether of chloramphenicol according to the procedure of Example 2.

Example 5 .Additional his and mono-O-silyl ethers Following the procedures of Examples 3 and 4, but substituting the triethylchlorosilane by tri-n-propylchlorosilane, tri n butylchlorosilane, tripentylchlorosilane, trihexylchlorosilane, triphenylchlorosilane and tribenzylchlorosilane, there are obtained respectively the corresponding compounds: bis O (tri n propylsilyl) chloramphenicol, mono (tri n propylsilyl)- chloramphenicol, bis O (tri n butylsilyl)chloraamphenicol, mono 0 (tri n butylsilyl)chloramphenicol, bis 0 (tripentylsilyl)chloramphenicol, mono O- (tripentylsilyl)chloramphenicol, bis O (trihexylsilyl) chloroamphenicol, mono O (trihexylsilyl)chloramphenicol, bis O (triphenylsilyl)chloramphenicol, mono O (triphenylsilyl)chloramphenicol, bis O (tribenzylsilyl)chloroamphenicol, and mono 0 (tribenzylsilyl)chloramphenicol.

Example 6 .-A dditional silylethers Also following the procedure of Examples 3 and 4, but substituting the triethylchlorosilane by dimethylchlorosilane, diethylchlorosilane, di n propylchlorosilane, din butylchlorosilane, dipentylchlorosilane, dihexylchlorosilane, diphenylchlorosilane, and dibenzylchlorosilane, there are obtained the corresponding bis and mono O (dialkylsilyl)chloramphenicols and the corresponding bis and mono O (diarylsilyl)chloramphenicols.

Example 7 .--A dditional silyl ethers Mixed monochlorosilanes, such as dimethylethylchlorosilane, methylethylpentylchlorosilane, methyltrin propylchlorosilane, methylethylchlorosilane, phenylmethylchlorosilane, diphenylmethylchlorosilane, benzylphenylchlorosilane and the like are used to prepare the corresponding bis and mono(alkylsilyl) and (alkarylsilyl) compounds included within the scope of the concept and practice of the invention.

The novel silyl ethers, in effective amounts for antimicrobial and anti-infective action, are compounded into pharmaceutical compositions for oral and injectable use, for example, tablets, suspensions, granules, emulsions, capsules, syrups and elixirs; sterile oil dispersions, sterile aqueous suspensions and sterile powders for injection; and the like. In such compositions, pharmaceutical carriers, i.e., compatible excipients, diluents, preservatives and the like are used to form compositions consisting essentially of the respective silyl ether. Unitary dosage forms suitable for providing anti-infective action in mammals are preferred. They generally contain from about 125 mg. to about 1000 mg. of the essential active ingredient per solid unitary dosage form and from about 2.5% to about 40% by weight of liquid unitary dosage forms.

These amounts are effective for anti-infective action.

The following pharmaceutical compositions are preferred embodiments of a pharmaceutical composition utilizing the silyl ethers of this invention.

Example 8.A queous suspension Ten liters, each ml. containing 60 mg. of mono(trimethylsilyl)chloramphenicol, is prepared according to the following formula:

Mono(trimethylsilyl)chloramphenicol gm 600 Preservative gm l0 Glycerin ml 3000 Tragacanth powder gm 100 Purified water, U.S.P., q.s. ad ml 10,000

The suspension provides an essentially tasteless preparation in contrast to the usually orally administered chloramphenicol.

Example 9.0il solution levels of active ingredient.

The foregoing anti-infective pharmaceutical compositions are exemplified using the mono and bis(trimethylsilyl)ethers of chloramphenicol. For these ethers, the other described silyl ethers of chloramphenicol are substituted in equivalent amounts to provide additional anti-infective pharmaceutical preparations with like beneficial results.

What is claimed is:

1. Essentially pure crystalline compositions of matter of the formula II NH-C 0 CH0]: Nor--c :-homom 6R1 Ill: where R is the moiety R: -SiRl wherein R and R are selected from the group consisting of lower alkyl containing 1 to 6 carbon atoms, inclusive, phenyl and benzyl, and R is selected from the group consisting of lower alkyl containing 1 to 6 carbon atoms, inclusive, phenyl, benzyl, and hydrogen; and R is selected from the group consisting of hydrogen and the moiety a -SiR4 u wherein R R and R are as given. I

2. Essentially pure crystalline composition of matter according to claim 1 wherein R and R are trimethylsilyl.

3. Essentially pure crystalline composition of matter according to claim 1 wherein R is trimethylsilyl and R is hydrogen.

No references cited.

TOBIAS E. LEVOW, Primary Examiner.

J. P. PODGORSKI, Assistant Examiner.

US. Cl. X.R. 424-324 

1. ESSENTIALLY PURE CRYSTALLINE COMPOSITIONS OF MATTER OF THE FORMULA 